This invention relates to a catalyst for preparing gases rich in methane by reacting hydrogen with carbon monoxide. Further, the invention relates to a process for preparing such a catalyst, and to a process for reacting hydrogen with carbon monoxide to form methane in the presence of such a catalyst.
The conversion of carbon monoxide or carbon dioxide and hydrogen to methane is known. In a prior art method, a mixture of carbon monoxide or carbon dioxide and hydrogen is contacted with a catalyst comprising a mixture of a carbonaceous solid and an alkali metal compound at a temperature between 427.degree. C. and 816.degree. C.; see U.S. Pat. No. 3,958,957. One particular problem associated with the use of such high temperature catalysts is that the methanation reaction itself is considered to be a combination of several reactions including the primary reaction EQU 3 H.sub.2 + CO .fwdarw.CH.sub.4 + H.sub.2 O (1)
and secondary reactions (2) and (3) EQU 2 H.sub.2 + 2CO.fwdarw.CH.sub.4 + CO.sub.2 ( 2)
4 h.sub.2 + co.sub.2 .fwdarw.ch.sub.4 + 2h.sub.2 o (3)
whose thermodynamic equilibria are such that the equilibrium yield of methane is adversely effected at high temperatures, i.e., above 500.degree. C. Accordingly, it would be highly desirable to develop an active catalyst system for methanation at temperatures below 500.degree. C. that would at least in part avoid the difficulties referred to above.
U.S. Pat. No. 3,842,121 discloses contacting a mixture of hydrogen and carbon monoxide at normal temperature and pressure with a catalyst comprising a complex compound of (a) at least one alkali metal belonging to Group IA of the Periodic Table, (b) at least one halide of a transition metal selected from the group consisting of Group IVB, VB, VIB, VII and VIIIB of the Periodic Table and (c) graphite. U.S. Pat. No. 3,842,113 discloses contacting hydrogen and carbon dioxide with a catalyst comprising at least one alkali metal belonging to Group IA of the Periodic Table, graphite and at least one halide of a transition metal selected from the groups consisting of Group VIB and VIII of the Periodic Table under normal temperature and pressure. In both of these processes, however, C.sub.2 hydrocarbon, such as ethylene and ethane are the major reaction products.
In accordance with the present invention, it has now been found that high yields of methane can be obtained at temperatures substantially below 500.degree. C. by contacting a gaseous reactant mixture comprising carbon monoxide and hydrogen with a catalyst consisting essentially of an alkali metal, activated carbon and at least one halide of a transition metal selected from Group VIII of the Periodic Table.